The present invention relates to a safety device for a municipal or similar gas supply pipe.
Earthquakes are a major hazzard in a number of areas of the world. While the earthquakes themselves cause major damage, the damage is greatly compounded by secondary explosions and fires. For this reason, it is of extreme importance to limit earthquake damage by preventing, as much as possible, these secondary explosions and fires which take such a tragic toll in lives and property.
One means of preventing explosions in municipal gas systems has been devised which automatically shuts off the gas supply to users when an earthquake, fire, gas leak or the like is sensed. The system provides automatic shutoff valves to the users' gas pipes which are triggered by an electrical signal from an earthquake, fire or gas leak sensor to close thereby shutting off the gas supply downsteram of the valves. It has been found in practice that this system significantly contributes to reducing the total damage caused by earthquakes and also explosions caused by gas leaks.
However, an important safety element is missing in the system described above in that gas explosions have occured after the earthquakes are over. The reason for this is that since the automatic shutoff valves shut off the gas supply to heaters, stoves and the like in individual homes, they necessarily extinguish the pilot lights. When the gas supply is restored, the gas supplied to the heaters is not immediately combusted due to the absence of a pilot light and accumulates in the area of the heater. The gas accumulation itself is deadly to persons exposed thereto and may be combusted by a spark in a refrigerator compressor motor, a lighted match or any other small heat source resulting in a disasterous explosion. The gas accumulation may also be ignited by the person relighting the pilot light, practically ensuring the person's fatality in the resulting explosion.